Paper manufacture



Feb. 2, 1932'. J. TRAQUAIR PAPER MANUFACTURE Filed Dec. 29, 1928 3 Sheets-Sheet 1 INVENTOR Q ATTORNEYS PAPERMANUFACTUR E Filed Dec. 29, 1928 3 Sheets-Sheet 2 W 1- nu.

ATTORNEYS Feb.2,1932. A J. TRAQUAIR 1,843,466

BAPER MANUFAQTURE Filed Dec 29, 1928 a Sheets-Sheet s mg VENQTOIR are WM A TTORNE Y S Patented Feb. 2, 1932 UNITED STATES PATENT OFFICE JOHN TRAQUAIR, OF C'HILLICOTHE, OHIO, ASSIGNOR TO THE MEAD RESEARCH ENGI- NEERING COMPANY,

OF DAYTON, OHIO, A CORPORATION OF OHIO IPAPEB MANUFACTURE Application filedDecember 29, 1928. .Serial No. 329,080.

This invention relates to the manufacture of paper and the like from cellulose containing materials, ration of pulp to ture.

One of the principal objects of the invention is to provide a method of treating fibrous materials to produce a superior pulp product which may be formed into a'paper having strength, color and other characteristics superior to the corresponding characteristics in paper formed from the same fibrous materials in other generally known ways previously used.

Another object of the invention is to provide a method of treating fibrous materials, such as straw, reeds,- fibrous grasses, cane, bamboo and the like, to produce high-grade paper, such as book paper.

Still another object of the invention is to provide such a method which is capable of continuous operation, is. self-contained, easily controlled, admits of recovery of the chemicals and avoids waste, is economical,

be used in such manufacand capable of producing good yields of highgrade paper from fibrous materials heretofore considered lower grade or inferion' Still another object of the invention is to provide apparatus for carrying out the above method.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and ap ended claims.

11 the drawings, in which like characters of reference are designated by like numerals throughout the several views thereof Fig. 1 is an elevational view, somewhat diagrammatic, of apparatus for carrying out the method of this invention;

Fig. 1 is a detail view in horizontal section of the steeping tank taken on the plane of the line 11 of Fig. 1, and showing the falsebottom of the tank in elevation;

Fig. 2 is an elevational view, somewhat I diagrammatic, of another portion of apparatus, Figs. 1 and 2 when placed end to end disclosing the complete apparatus;

Fig. 3 is a view similar to Fig. 2 showing a somewhat modified form of'apparatus:

and particularly to the prepa-v designed 'to handle such materials.

I paper.

Fig. 4 is a diagrammatic end view of the steeping tank and expeller; and

Fig. 5 is a diagrammatic end view of the blow pit and make-down chest.

The method of the present invention lends itself particularly to the treatment of straw, cereal grasses, cane, bamboo, reeds and the like, in the manufacture of high-grade. paper, and the apparatus illustrated is particulajrllly term straw as hereinafter used is not meant to be a limitation but as merely designating all such analogous materials. The method and apparatus are also applicable to the treatment of wood.

Certain types of fibrous materials, such as straw, have heretofore been considered inferior for the manufacture of high-grade paper and have not been generally so used. In materials such as straw, an inordinately large proportion of the fibrous material is destroyed or lost by the heretofore generally used methods of pulping, if the hard -fiber bundles or shives are sufliciently defibered to permit of securing a final pulp at all suit able for the manufacture of high-grade The cooking actions generally used heretofore result in low yields with such materials, and the strong cooking liquors at high temperatures and pressures attack the cellulose fibers reducing heir strength. Even with comparatively drastic cooking treatment, an objectionable proportion of hard fiber bundles or shives remains in the pulp stock. The present invention provides a method of treating fibrous materials, and particularly straw, to give a pulp stock of good strength and color with a good yield, while at the same time the consumption of chemicals is maintained at an economical point. I

Referring to the drawings, apparatus constituting a preferred embodiment ofthis invention, and which is adapted for carrying out the method of this invention, is diagram- 'matically illustrated. Bales of straw are 7 used, such as solutions of caustic 11, the bales are broken open before being fed into the duster mechanism 13, which may be of the conventional type used in the industry for dusting old papers, and needs no further illustration here. Toothed rolls 14 are provided for subdividing the straw and feeding it into the duster. The loose dusted straw feeds through a discharge chute 15 directly into a feeding hopper 16 of a steeping tank 17. A spray pipe 18 suitably perforated on the under side is adapted to spray hot caustic liquor upon the straw as it feeds into the hopper'16 to thereby wet the straw to facilitate its passage into the steeping tank 17. The supply pipe 18 is connected with a suitable source (not shown) of alkaline liquor. The wall 20 of the feeding hopper 16 is inclined downwardly and feeds the straw into a positive feeding-screw 21 carried by a shaft 22 driven from a pulley 23 and mounted adjacent the hopper 16.

An suitable form of steeping tank or cham r may be used, in which the fibrous material may be immersed or steeped in a liquor of controlled characteristics and at a controlled relatively low temperature and pressure such that the primary action is a softening of the bonding material holding the cellulose fibers together, while the cellulose fibers themselves are not objectionably affected. A mild caustic soda solution is preferred, but other alakline liquors may be potash, sodium carbonate, and the like.

As shown the tank comprises a casing 30 which is normally kept substantially filled with the steeping liquor. Within the tank is a perforated false bottom 32, the casing beneath the false bottom being inclined downwardly from the ends toward the center as indicated at 33, with a drain pipe 34 controlled by valve 35 for withdrawal of liquor. Passing through the inlet end of the tank is a shaft 36 supportedrat one end by a stuffing box and bearing 37 and at the opposite end by a bearin 38 carried by the end wall of the tank. The shaft 36 carries on the exterior of the tank a gear or pulley 39' which may be driven from any suitable source of power (not shown), and within the tank suitable means for forcing the steeping material toward the discharge, this means being illustrated as a helical screw 40.

At its outlet end which is open as indicated at 41, the steepin tank is provided with discharge means, w ich is shown as a bucket conveyor 48, running over a roll 47 carried by the shaft 36 within the tank and a second cooperating roll 50 elevated above the tank and to one side thereof and suitably mounted for rotation. A suitable drip trough 46 is positioned below the conveyor and drains into the tank. The elevator buckets 49 are perforated and preferably of wire and constructed somewhat in the form of a pitch fork having a plurality of curved rongs. The elevator is positively driven, an as-the buckets or forks conveying the steeped straw pass above the liquid level, the liquid retained therein drains rapidly back into the steeping tank. The upper end of the elevator 48 is so positioned as to discharge the steeped and drained material into'the feeding hopper 54 of an expeller indicated generally at 55.

Any suitable type of expeller which functions to remove excess liquor from the treated material and whereby a desired control of the consistency of the expelled material is effected can be used. As illustrated it comprises an outer cylindrical casing or shell 56 mounted in a suitable supporting framework, the discharge end 57 of the shell being inwardly tapered. Within the shell is a perforated screen 58 forming a false bottom, and operating within the screen is a rotar helicalscrew 59. One end of the shaft of the screw passes through a stufling box and carries on the exterior thereof a driving gear (not shown), which may be driven from any suitable source of power. The material discharged into the hopper 54 from the elevator 48 is fed through the casing by the helical screw 59. The decreasing diameter of the interior of the casing efi'ects a compression of the material forced therethrough which squeezes out a portion of the retained liquor, and this liquor passes through the perforate screen 58 into a discharge chamber 60 built up at the lower side of the casing. The expelled material is discharged through the open feeding end 62 by the screw 59.

The steeping liquor within the steeper 17 is preferably maintained hot, but below the boiling point. It is found that the time of steeping and the temperature of steeping are inter-dependent, the hotter the steeping liquor the less time'required for the proper softening of the straw. Very suitable results are secured by maintaining the stee ing liquor at a temperature of about 90 at which temperature objectionable steam formation which would readily escape into the room or building through the open steeping tank is avoided, and so proportioning the speed of screw conveyor 40 that the straw is allowed to steep for approximately half an hour to one hour. It is found that uite dilute steeping liquor functions satis actorily and satisfactory results with less resistant materials are obtained by steeping in as dilute a liquor as 1% NaOH or even less. The concentration may be varied between 1% and 6% with satisfactory results, but apparently increasing the concentration above 6% does not seem to produce advantages sufficient to make the increased concentration desirable. For wheat straw, a concentration of about 2% t0 3% gives very satisfactory results. A large excess of liquor relative to the quantity of straw is preferably used so that the satisfactory results are obtained when as much as twenty parts liquor are used to one part of straw, at which proportion the straw moves easily.

Any suitable means may be employed for maintaining the-steeping liquor at the proper temperature. In the present construction, the fresh caustic make up liquor which is introduced through the spray pipe 18 is preferably heated to about 95 6., and this serves to maintain the temperature at the inlet end of the steeping tank. In order to maintain the temperature adjacent the outlet end of the steeping tank, a recirculating and heating mechanism is provided. As shown, a portion of the liquor within the steeping tank is with-' drawn through the pipe 34 and passes through a conventional gravity filter 70. The

steeping liquor within the steeping tank functions not only to soften and wilt the straw but also washes it and removes sand and dirt and the like. These removed impurities which pass through the perforate false bottom 32 readily settle within the chamber 33 and are drawn off through the pipe 34 and thus removed by the filter 70. The liquor expelled from the steeped material by the expeller 55 is withdrawn from the collecting chamber 60 through the pipe 71 and is added to the filtered liquor passing from'the filter 70 through the pipe 72. The pump 73 forces this liquor through a conventional heater 74 and thence through return pipe 75 which delivers into the steeping tank 17 somewhat nearer the outlet end as indicated at 76, to thus maintain the liquor in this end of. the tank heated to the desired temperature.

The height of the elevator 48 with consequent draining of the steeped material and the action of the expeller are so coordinated that a controlled amount of liquor remains in the expelled material. Very satisfactory results are secured when the steeped material is thickened at the expeller to a consistency of about 3 to 4 parts of liquor to one of straw. The fresh caustic liquor introduced through the pipe 18 may be regenerated liquor which comes from recovery. The liquor at the inlet end of the steeper thereby contains the highest percentage of causticity, while the liquor at the outlet end of the steeper has its caus ticity largely exhausted or spent, such a concentration gradient bein maintained that at time of discharge the 'fiquor still contains, about 15% to 35% of its original causticity.

The expelled material with retained liquor is discharged from the expeller into a feeding hopper 8O feeding into a screw conveyor 81 having a shaft 82 carrying a helical screw 83 and a driving pulley or gear 84. The discharge 85 of the screw conveyor 81 feeds into a hopper 86 positioned to discharge into the filling opening 87 of a conventional digester 88 provided with a movable cover 89 for the filling opening. The cover 89 may be carried by a. breech block mounting so that this cover may be readily swung back to uncover the filling opening for the filling operation, and then may be quickly swung into place to effectively seal the digester during the subsequent steaming operation. The digester is provided with a relief valve 91, a discharge pipe 92 opening out of the lower conical end 93 thereof and controlled by a blow-ofi valve 94, and with a steam introduction pipe 95 controlled by valve 96 and having a plurality of tr at such high density effects an economy in the operation in that much larger'quan tities of the material can be treated at one time than in the ordinary practice where fibrous material is cooked with a large quantity perforate openings 97 throughout the pipe of strong coking liquor. After filling of the digester, the removable cover 89 is closed and steam is introduced through the pipe to raisethe temperature of the mass within the digester to a temperature and pressure materially higher than in the steeping stage, and to maintain that temperature and pressure for a period of time to complete the reaction between the retained liquor and the fibrous material. This multi-stage cooking treatment is highly effective in securing the resolution of the fibrous material without objectionably affecting the cellulose. The material is thus subjected in one stage to a controlled treatment or steeping with a relatively concentrated liquor at a sufiiciently low temperature and pressure to effect softening of the fibrous material without deleteriously affecting the fibers. The material is then subjected in another stage to controlled treatment in the presence of a relatively less active or dilute liquor at a much higher temperature and pressure such that loosening of the fibers is adequately effected but without objectionable injury to the fibers. For purposes of easy description, that concentration of liquor'which if exceeded at a given tem perature and pressure will injuriousl the cellulose fibers is herein termed a critical concentration, and that temperature and pressure'whichif exceeded for a given concentration of liquor will injuriously affect the cellulose fibers is herein termed a critical temperature and pressure. The major porterial is then further effected in the digestion stage at a much higher temperature and pressure with a liquor of controlled concentration below the critical concentration.

By carrying out the separate stages in differ- 5 ent vessels, the advantages of the continuous treatment in the steeping stage at low consistency, and the packing of the material at high consistency into the digester in the digestion stage, are obtained. The digester is preferably heated to a temperature of about 170 C. to 190 C. or higher and to corresponding pressures by the introduction of steam, but temperatures and pressures below this may be used with decreasing effectiveness. In the presence of the largely spent liquor, such temperatures and pressures may be used Without objectionably affecting the cellulose, while effective reaction and resolution of the incrustants are obtained. Very satisfactory results have been secured by the introduction of steam in such a manner as to raise the temperature of the mass in the digester toabout 180 C. and to a corresponding pressure in substantially half an hour, and to maintain this temperature and pressure for another'halt' hour to one hour. The blow-off valve 94 is then opened and the digester'blown against the impact plate 100 positioned within the usual housing 101 with steam escape stack 102 to eifect pulping of the fibrous mass. Preferably two or more digesters are provided, one digester being filled while the digesting operation is being carried on in another. A second digester may be conveniently provided to discharge against the opposite side of the impact plate 100.

After the blow, the pulped mass settles into the lower conical part 103 of the housing 101 while the steam and other vapor escape through the stack 102. A swiveled discharge spout 104 is provided to distribute the pulped mass into the blow pit 105. Any suitable construction .of blow pit may be provided. Preferably the blow pit is constructed to secure an even and controlled feed of the pulped mass to the make-down chest 106. As shown, the bottom of the blow pit 105 is pro- 50 vided with a plurality of transverse openings or passages 107, each of which is normally closed by a pivoted gate 108, which may be pivotally mounted at one side of the blow pit as indicated at 109. Each of the pivoted gates 109 may be provided with a chain or other flexible cord 110 which passes over a pplley 111 to a suitable control center. ere any suitable provision mayv be made for the selective or simultaneous operation 60 of the pivoted gates 109. The'make-down chest 106 is preferably formed with side walls which converge downwardly, being shown as V-shaped in cross-section, and a feeding screw 115 carried on a shaft 116 mounted in 06 hearings in the make-down chest and provided with a driving pulley or gear 117 is located in the lower portion of the chest. A suitable pipe 118 supplies make-down li uor to the pulp discharged from the blow plt, and the feeding screw 115 feeds the diluted pulp mass into a mixing chest 119 supplying a pump 120 which forces the stock through a pipe 121. a

The pipe 121 feeds into the central compartment of a conventional head box 125 which is provided with an overflow partition 126 by which the excess of stock pumped thereto may be discharged into a return pipe 127 and fed back into the chest 106. The head box is also provided with a second partition 129 having a sliding gate or weir 130, so that a controlled amount of the stock may be discharged through a chute 131 into a conventional mixing box 132 having a plurality of staggered'bafiies 133 to thoroughly mix the stock passing therethrough. The mixing box 133 discharges into a pipe 136 which feeds into an open tank 137. Rotatably mounted and'dipping within the stock within the tank 137 is a rotary vacuum filter indicated at 138. This rotary filter may be of any conventional construction, for example, of the type known commercially as the Oliver filter, such filters being well known in the art and so not particularly illustrated herein. This filter 138 comprises a perforate rotary screen divided into compartments of definite suction areas. The screen dips into the stock within the tank 137, the suction causing the fibrous material to accumulate on the surface of the screen as the liqilor passes therethrough into the interior. As the screen rotates carrying the filtered layer above the liquid level within the tank, sprays of washing liquid are directed thereon from suitably disposed spray pipe 1 10. The material thus washed is practical- 1y freed of the substantially spent treating liquor, which may be termed black liquor. As the filter continues to rotate, the material which has been thus washed arrives at an area which is not subject to suction,-and at this point a flexible scraper member 141 fastened to the side of the tank 137 scrapes this material from the filter causing it to slide down the member 141 over the edge of the tank 137 into a chute 142.

As the fibrous material/accumulates upon the screen of the rotary vacuum filter 138, the black liquor is sucked through into the interior of the filter, ahd the remaining black liquorin' the fibrous material is washed out by the sprays-directedupon the fibrous mate- -rial so that the black liquor is substantially all removed from the fibrous stock. Prefers ably controlled amounts of spray are added to the fibrous stock upon the filter, so that the black liquor is substantially all washed out, the washing liquid taking its place, but

so that unnecessary dilution of the black liquor is avoided. The black liquor sucked throughiout the system. The recovery plant from the fibrous material to the interior'of the filter 138 passes by the pipe 144 to the vacuum tank 145 of conventional construction such as used with rotary vacuum filters of this char: .cter. A suction pump 146 connected to the upper part of the interior of the tank 145 by pipe 147 furnishes the suction for the Oliver filter 138. For withdrawing the black liquor from the vacuum tank 145 against suction existing therein, a pipe 148 is tapped into the bottom of the vacuum tank 145, and

a centrifugal pump. 1491s positioned within the pipe 147"The pump 149 discharges into a'pipe 150, which in turn discharges into the central compartment of a second head box 151 similar to the head box 125 The head box 151 is provided with an overflow partition 152 whereby the excess of black liquor is discharged into pipe 118 feeding into the 0 make-down chest 106 The black liquor thus removed from the fibrous stock in the rotary vacuum filter is returned to the chest 106 to make down or dilute the stock therein to a consistency such that it can be readily pumped or flowed through pipes. About 5% is a satisfactory consistency for this purpose. By making down the stock within the chest 106 with spent black liquor, rather than with fresh 0 water, the black liquor is not diluted. Preferably the stock is further diluted before passing into open tank 137 of the rotary vacuum filter 138. For this purpose a pipe 155 is tapped into the pipe 150, the pipe 155 discharging at 156 into the top of the mixing box 132. A valve 157 is provided to control the flow through pipe 155. Satisfactory results are obtained by making down the stock to a consistency of about 1% to 1 before passing through the rotary vacuum filter.

The head box 151 is also provided with a second partition 160 having a slidable gate or weir 161. In this manner controlled amounts of the black liquor pumped to the head box 151 are discharged into a pipe 162 which leads to a recovery plant indicated diagrammatically at 163. The amount of black liquor discharged to recovery is preferably comparable to the amount of liquogcar- 5Q ried by the steeped expelled material. And likewise the amount of fresh regenerated caustic liquor introduced from recovery into the steeping tank is preferably comparable to the amount of-liquor removed from the :3 steeping system. which is that amount re- .tained in the fibrous material after expelling. The amount of black liquor discharged to recovery thereby is comparable to the amount of fresh caustic, liquor introduced on into the steeping tank. In this manner, the

as it may be of entirely conventional form, such as used inthe recovery of black liquor formed in the digesters in the manufacture of soda pulp, the steps of which are well known and consist essentially of evaporation of the liquor, burning of the residue to black ash, the lixiviation of the black ash, and the causticization of the extracted liquor. From the recovery plant 163, a pipe 164 leads the regenerated or active caustic liquor through a conventional heater indicated at 165 to the spray pipe 19. Thus a self-contained process forthe manufacture of paper forming stock from straw is rovided, in which the chemicals used can e recovered so that there is little loss of chemicals in the process and stream polution is avoided.

The pulped mass thus produced, especially when prepared from straw and analogous materials, containsasubstantialproportionof shives andhardbundles of fibers which render the pulp unsuited in its present condition for the production of high-grade paper, such as book paper. In accordance with this invention, this alkaline treated pulp is subjected to a chlorination treatment for the purpose of completing the pulping of the material and breaking down the hard bundles of fibres and shives. Where a large proportion of'the ligneous and other bonding materials holding the fibers together are removed in the steeping and pressure digestion treatment, such as where the remaining ligneous and other 'incrustant materials amount to only' about 5% or less of the cellulosic content, a chlorination with a strong chlorinating agent, such as chlorine gas, may be given the pulp directly without obj ectionable temperature rise or hydrochloric acid formation such as to deleteriously affect the cellulose fibers. In this case, the fibrous mass is first thickened and rendered permeable to gas and is then subjected to the action of a gaseous 'chlorinating agent whereby the pulping or disintegration of the fibrous material into its ultimate fibers is completed to form a satisfactory high-grade pulp. In this phase of more drastic action, in which a high chlorine concentration is effective in the fibrous mass, the chlorine reacts with the more resistant ligneous matter with consequentresolution ofthe shives or other underfibered material.

Duringsuch reaction the ligneous and other material in the 'shives, or the like, is apparently changed by the action of the chlorine gas into compounds which may be readily washed outwith alkaline solutions such as caustic soda;' or which, even if not fully washed out are of such character as to color and other characteristics as to be substantialliquor is maintained in controlledamoums ly unobjectionable and-"ineffective to lower is adapted to treat the spen't'liquor'to regenerate the same to form'again active caustic liquor. The plant is not illustrated herein the qua1ity of the resulting pulp.

Very satisfactory results are secured in this chlorination treatment with consistencies of substantially 15% or higher, at which con= chai es into a hopper 184 which feeds into sistencies the stock is permeable to gas. The pulp mass discharged from the filter 138 into the-chute 142 is generally at a consistency of about 8% to 10%. The discharge of the chute 142 is positioned to feed into a further thickening device indicated generally at 170 where the stock is dewatered to a consistency of substantially 15% or higher, preferably 20% to 30%. Any suitable type-of continuous thickener may be used for this purpose, such as cylindrical thickeners with pressure rolls to regulate the water content of the stock, rotary vacuum filters, or centrifugal thickeners. The machine illustrated is of the continuous centrifugal type and comprises an inner distributing rotor 171 having a spiral flange 172, the rotor being keyed to a shaft 173 driven by' a motor 174, and a second rotor or perforated filtering screen 175 carried by a sleeve 176rotatably mounted u on shaft 173 and also driven from motor 1 4 through suitable gearing at a speed which is preferably slightly less than the speed of the rotor 171. The outer screen is surrounded by a stationary annular trough 177 forming an enclosing casing. The chute 142 continuously feeds the stock into the space between the inner rotor and the outer filtering screen, where it is carried through the ma- .chine by the spiral flange 172 while being subjected to such centrifugal force as to cause a portion of the retained water in the pulp to pass throu h the filtering screen 175 into the trough 17 from where the filtrate is removed by pipe 178.

The dewatered stock discharged from the centrifugal machine is fed by a chute 180 ton supply trough 181 from where it is scooped by an endless bucket elevator 182 and fed into a treating tower 183 constructed of acid and chlorine proof material. As shown diagrammatically herein, the elevator 182 disa screw conveyor 185 having an opening 186 on the lower side thereof opposite the open upper end 187 of the tower 183. Stock feeds through the opening 186 into the upper end of the tower 183 as needed to maintain the tower full of stock, the surplus stock handled by the screw conveyor 185 being discharged at the end 188 and returned to the source of supply. The tower 183 is provided with an inlet 190 for a controlled supply of chlorine gas, and controlled outlets 191 and 192 for the discharge of gas. The gas discharging from the tower, which contains some free chlorine, is preferably passed to recovery apparatus, (not shown) such as a water absorption system. Water or other slushing liquid is introduced adjacent the base of thetower at 194 to dilute and slush out thes'tock through the water-sealed bottom 195 of the tower into a trough 196, thestock passing from the upper end to the lower end of the tower by gravity in accordance with the rate at which it is The stock may be fed from the trough 196 i to a storage tank, or it may be passed directly to further treating apparatus. As shown, the stock discharges through a pipe 198 into a solvent tank 199. Here it is mixed with a controlled quantity of alkali, continuously supplied from a pipe 200. The tank 199 is constructed to effect a continuous and uniform treatment of the material passing therethrough, and to secure a thorough mixing of the fibers with the solvent alkali. For this purpose, the tank is provided with a plural- 1ty of staggered baflies 201 which provide a circuitous flow of the material from the inlet 202 to the-discharge 203 connected to the suction side of a pump 204. The first compart-ment of the tank 199 is preferably provided with suitable agitating mechanism such as a driven shaft 205 having a plurality of rotary stirring arms 206. The capacity of the tank 199 is such that the treated material is allowed to remain about half an hour therein, this giving sufficient time for the reaction products of the chlorination to be dissolved. Any suitable alkali may be used for this purpose, dilute cold solutions of caustic soda sodium carbonate, or sodium sulphite giving very satisfactory results.

The pump 204 feeds the dilute stock through a pipe 208 to a continuous filter mechanism 209 which serves to wash and thicken the treated material. This filtering mechanism may be a conventional rotary vacuum filter, such as an Oliver filter, similar in construction and operation to the filter 138. The stock from pipe 208 together with suflicient water to make down to a consistency of about 1% is discharged into tank 210, and suction within the compartments of the screen causes the fibrous material to accumulate on the surface of the screen as the water passes into the suction compartments. As the screen rotates carrying the filtered fibrous material above the liquid level within the tank, sprays of wash water or dilute alkali are directed upon the material from spray pipes 211. The dissolved reaction products of the chlorination and the excess alkaline liquor are thus washed out of the stock, while controlled suction draws liquor from the fibrous layer. As the filter continues to rotate, the material which has thus been washed and thickened rotary shaft 218 with agitating arms 219,

are provided. The tanks are arranged at successively lower elevations, and the bottom of a preceding tank is connected to the upper end of a succeeding tank by a pipe connection 220. Each connection 220 has its highest point located below the level of the stock in the preceding tank, whereby a head is effective to secure a flow through the pipe. The

capacity of the tanks is such as to insure suflicient time for the completion of the final bleaching action during the time the material flows through the connected bleaching tanks. A suitable bleaching agent, such as bleach liquor, sodium hypochlorite, or chlorine water is continuously added by pipe 221. Due to the eflective chlorinating action, the quantity of bleach required is very materially reduced, approximately 1% to 3% of bleach liquor on the dry weight of the pulp being suflicient to produce a pulp having a highwhite color. The bleached pulp continuously discharging from the last tank 217 through pipe 222 is forced by a pulp 223 to a second rotary vacuum filter 224 similar to the filter 209 where the pulp is washed and thickened. The treated pulp is then discharged through chute 225 into a stock chest 226 where it is stored for further treatment or for use.

Where the initial steeping and pressure digestion treatment does not remove a sufficient percentage of the ligenous or other bonding materials in the fibrous material so that such materials remaining in the pulp constitute more than about 5% of the cellulosic content, it is found preferable to subject the pulp mass to a two-stage chlorination plished by diluting the fibrous stock to a low consistency. In such case the water in which the fibers are suspended apparently serves as a heat absorbing mediumto avoid an objectionable temperature rise with injury to the fibers. The water also serves to dilute the hydrochloric acid formed in the reaction, thus additionally diminishing objectionable results. 7 Very satisfactory results have been secured with consistencies below 5%. Such low consistencies at the same time provide a fluid mass which may be readily pumped or gowed through conduits or treating chamers.

This first stage of the chlorination is pref erably continuous, the dilute stock being subjected to chlorination as it passes through the apparatus. The amount of chlorinating agent utilized is continuously controlled, preferably in an amount insuflicient for complete chlorination. As a result the more readily chlorinated material first reacts with the chlorinating agent in a comparatively short time as the mass flows along. The amount of chlorinating agent however is preferably controlled to be as much as will be readily taken up by the fibers in this short treating period, while insuring substantially complete reaction. This initial reaction is rapid, and it has been ascertained that the reaction of about 85% of the chlorine required for complete chlorination of a given fibrous mass goes to substantial completion in about fifteen to twenty minutes. Generallythe addition of about 65% to 95% of the chlorine needed for complete chlorination in the first stage with a treating time of about half an hour gives very satisfactory results.

Various chlorinating agents may be used for this first stage such as chlorine, sodium hypochlorite, bromine, and the like, chlorine being preferred due to resulting economy and ease of control. The use of ordinary bleach or other calciumcompounds at this point is found objectionable due to the formation of insoluble calcium reaction compounds in the pulp which are not readily washed out in the subsequent alkali washing treatments. The chlorine may be added'at a controlled rate in the form of chlorine water. :Or a chlorine water solution may be added to the water in which the fibers are suspended to provide the desired consiestency. Or chlorine gas may be introduced at a controlled rate directly into the fibrous stream which has previously been made down to the desired low consistency.

As shown in Fig. 3, the chute 142 from the Oliver filter (as disclosed in Fig. 1) discharges into a length of pipe 250 having a spiral baflle 251 therein. A controlled supply of chlorinatng agent, such as chlorine water, is introduced into the stream of fibrous material by pipe 252 which has a control valve 253. The spiral bafile 251 creates a turbulence in the flowing stock stream serving to mix the chlorinating agent with the pulp mass, and the fibrous mass and chlorinating agent pass together from the mixer into a. chlorinating tank'or chamber 255.

The chlorinating tank 255 is constructed of acid proof material such as tile or concrete and is divided into a plurality of connected chambers or compartments, represented in the drawings by two chambers 256 and 257 divided by a central partition 258. The mixed mass and chlorinating agent flow downwardly through space 256, beneath the lower end of the partition 258, and up through the space 257 to the overflow pipe 259. The tank 255 is constructed of a capacity to accommodate 'suflicient material to provide the desired re conventional type of washing apparatus, shown diagrammatically as a worm-type drum washer. This comprises essentially an acid proof perforated rotor drum or screen 260 having an interior ribbon conveyor or spiral 261 and spray pipes 262 for spraying wash water upon the stock. The stock feeds into the interior of one end of the rotary drum and is carried continuously through as it is washed by the sprays and discharges from the other end. A part of the water in the stock drains through the perforated drum into a receiving tank 263 so that the stock generally discharges from the washer at a consistency of about 10% to 12%. The short time of treatment in the chlorination chamber coupled with the fact that free acid formed in the reaction is washed out immediately after chlorination further serves to prevent injury to the fibers. An additional spray pipe 264 is preferably provided to spray an alkaline solution, such as a dilute NaOH solution, upon the washed fibers to neutralize any acid or free chlorine remaining in the fibrous mass, thus avoiding the necessity for further acid proof apparatus as well as assisting in dissolving out reaction products of the chlorination. If desired, an alkaline steeping in addition to the washing may be given at this point, this being found advantageous in the case of fibrous stock which is less defibered.

The discharge 265 from the worm washer feeds into a centrifugal thickener 170', which in turn feeds into a chlorination tower 183 feeding into a solvent tank 199' similar to the construction illustrated in Fig. 2. The construction and operation of the balance of the apparatus of Fig. 3 including the Oliver filter and continuous bleacher, etc., is similar to that disclosed in Fig. 2 and so not further illustrated herein.

A finished pulp is produced in accordance with this invention which may be formed directly into a high-grade paper, such as book paper, which has unusual strength and purity and is of a high white color. Average yields of 45% by weight of bleached pulp on the dry weight of the original raw materials are obtained with straw. By a proper coordination between the preliminary steeping and pressure digestion treatments and the subsequent chlorination treatment, abalance may be struck between the consumption of soda and the consumption of chlorine with resultant economy in the process. For example, very satisfactory results are obtained where suflicient caustic liquor is added to the steeped material and the conditions of the steeping and pressure digestion are so controlled as to effect a total caustic consumption on the dry weight of the straw of approximately 10% to 12%. 'Assuming a yield of around 45%, this gives a total caustic consumption on the dry weight of the bleached pulp of approximately 25% to 30%. The recovery of the black liquor removed from thissteeped and pressure digested material further economizes in the process, a recovery of 80% of .the caustic content being easily accomplished in actual commercial operation. This gives an actual consumption of about 5% to 6% of caustic soda on the dry weight of the bleached pulp. With'such an initial steeping and pressure digestion treatment giving the above noted caustic consumption, it is found that an effective subsequent chlorination may be carried out with a low chlorine consumption, generally around 5% to 6% on the dry weight of the bleached pulp In this manner, substantially equivalent gram molecular weights of caustic soda and chlorine are consumed in the rocess. Thus an electrolytic cell plant treating a salt solution could be used advantageously to supply both the caustic soda and the chlorine with a substantially balanced supply of each.

The following is a typical example of a pulping treatment carried out in accordance with this invention. Raw fibrous material, such as wheat straw, is introduced into the steeping tank containing caustic soda liquor having thirty grams NaOH per liter (3% concentration). The speed of the helical screw is controlled to move the steeping material from the feeding end to the discharge end in about thirty minutes. The steeping liquor is maintained at a temperature of substantially 90 C. The steeped material is removed by the elevator and permitted to drain and then is introduced into the expeller and raised to a consistency of about 20% to 25%. The expelled material is charged at this high density into a digester and steam is introduced to bring the digester up to approximately 180 C. and to a corresponding pressure in approximately thirty minutes, and the digester is maintained at such a high temperature and pressure for about thirty minutes. The digester is then blown and the pulp stock washed to remove the black liquor and thickened. The stock is then further thickened in the centrifugal thickener to about 20% to 30% consistency and is fed to the chlorinating tower where it is passed through a maintained layer of chlorine gas for about fifteen to thirty minutes, sufficient chlorine being continuously introduced to supply about 5% chlorine on the dry weight of thefinished pulp. The chlorination is carried on at ordinary room temperatures. The chlorinated stock is then introduced into the alkali solvent tank with a sufficient quantity of cold 1% NaOH solution to render the mass distinctly alkaline, and is agitated and steeped therein for about half an hour. After washing and making down to about 5% consistency, the material is introduced into the bleacher with a quantity of bleach liquor suflicient to bring the consistency to about 4% to 5% and to pro-' vide about 3% bleach liquor on the dry weight of the pulp. The flow of stock through the bleacher is controlled to provide a. treating time of about one hour or more. The bleached pulp is then washed and thickened and dropped to-a stock chest where it is ready for use or further treatment.

Where a two-stage chlorination is given, the washed and thickened pulp coming from the digester is first diluted to a low consistency. Chlorine water containing approximately 80% to 90% of the chlorine required for complete chlorination of the pulp is preferably added. The chlorine is added to the stock in the form of a solution in water containing approximately 2% to .4% chlorine, or is added directly as chlorine gas. In the former case the raw fibrous material is made down to a consistency of about 4% to 6%, the addition of the chlorine water bringing the consistency to about 1% to 4%. In the latter case the consistency of the material is made down initially to about 2% or even less. The rate of flow. through the chlorination chamber is controlled to give a treatingtime of about half an hour. The stock is then washed and after thickening to about 20% to 30% consistency is then subjected to the gas chlorination, alkaline solvent and bleaching treatments as above described. I

While the initial steeping followed by the pressure digestion generally permits a sin-, gle gas chlorination to be effectively used without deleterious results, with some types of raw cellulosic materials an alkaline steeping followed directly by a two-stage chlorination may be used to produce a good grade of pulp although the chlorine consumption is generally high.

For urposes of" easier description, the expression annual growth fibrous material is used herein to denote the various types of straw, grasses, and other fibrous materials of large packing volume, which because of their bulk are diflicult topack in their initial state in a digester and aredifiicult to efiectively cook when so packed and submerged in liquor therein, and which substantially shrink in. packing volume upon an initial steeping, as distinguished from hard and compact pieces or chips of wood. which do not substantially shrink in pacln'ng volume upon an initial steeping.

While the methods herein described, and the forms of apparatus for carrying these methodsinto effect, constitute preferredem bodiments of the invention, it is to be understood thatthe invention is not limited to these precise methods and forms of apparatus, and

that changes may be madetherein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

jter, means for raising'sai 1. Apparatus of the character described, comprising in combination, a steeping tank having an inlet adjacent one end and an outlet adjacent the other end.thereof, means for introducing fibrous material into said inlet, means for introducing a steeping liquor into said tank, means for effecting heating of the mass within said tank, means for. moving fibrous material from said inlet toward said outlet of the tank and for removing steeped fibrous material from said outlet of the tank, a digester, means for introducing fibrous material removed from said steeping tank into said digester, and means for heating said digester to a higher temperature and for raising the pressure therein.

2. Apparatus of the character described, comprising in combination, a steeping tank, means for introducing fibrous material and steeping liquor into said tank, means foreffecting heating of the mass within said tank, means for removing steeped fibrous material with retained liquor from said tank, an expeller, means for passing the removed material through said expellerto remove a portion of the retained liquor from said material, a digester, means for introducing the expelled fibrous material with the retained liquor into said digester, and means for heating said digester to'a high temperature and for raising the pressure therein.

3. Apparatus of the character described,

comprising in combination, a steeping tank,

means for introducing fibrous material and steepmg liquor into said tank, means for removing the steeped fibrous material from said tank, an expeller, means for passing said removed material through said expeller to remove a portion of the retained liquor therefrom, a heater, and means for returning the liquor removed by said expeller to said steeping tank through said heater.

4. Apparatus of the character described, comprising in combination, means for admixing fibrous material and steeping liquor and for heating the admixed mass at a relatively low temperature and pressure to efi'ect controlled reaction therebetween, a digester, means for introducing the fibrous material admixed with retained liqayor into said digesdetermined higher temperature and pressure, a chlorination chamber having provisions for circulation of material supplied thereto,

mean'sj for introducing the material discharged from said digester into said chlorination chamber, and means for introducing a chlorinating agent into said chlorination chamber.

5. Apparatus of the character described, comprising-in combination, a steeping tank means for introducing fibrous material an alkaline liquor into said tank, means for heat- .ing the mass within said tank at a relatively low temperature and pressure to efiect condigester to a pretrolled reaction between said fibrous material and alkaline liquor until the alkalinity of said liquor is primarily exhausted, means for removing the steeped fibrous material with retained liquor from said tank, a digester, means for introducing the removed fibrous material with retained liquor into said digester, means for bringing said digester to a predetermined higher temperature and pressure, means for blowing said digester, a chlorination tower, means for introducing the blown fibrous material into said tower,

and means for introducing chlorine gas into said tower.

6. Apparatus of the character described, comprising in combination, means for admixing fibrous material and steeping liquor and permitting reaction therebetween, a digester, means for introducing the fibrous material with retained liquor'into said digester, means for raising the temperature and pressure within said digester, means for diluting the material discharged from said digester, a chlorinating chamber, means for introducing the fibrous material diluted to low consistency and a chlorinating agent into said chamber, means for thickening said chlorinated material, a second chlorination chamher, and means for introducing the thickened material and a chlorinating agent into said second chlorination chamber.

7. In apparatus of the character described a steeping tank adapted to contain a steeping liquor, a feeding inlet therefor, a discharge therefrom, aperforated false bottom within said tank, and means above said false bottom for moving fibrous material from the feeding inlet toward the discharge.

8. In apparatus of the character described. a steeping tank adapted to contain a steeping liquor and having a feedin inlet and a discharge, means for feeding fibrous material into said feeding inlet, means within said tank for moving fibrous material from the inlet toward the discharge, elevating means for removing steeped fibrous material from the discharge and for permitting draining of the fibrous material, an expeller, and means for introducing the drained fibrous material into said expeller.

9. In apparatus of the character described, a steeping tank adapted to contain a steeping llquor comprising an elongated cylindrical casing, a feeding inlet adjacent one end thereof, a discharge adjacent the other end thereof, a perforated false bottom within said casing, said casing being inclined downwardly beneath said false bottom, and a liquor withdrawal pipe connected adjacent the lowest point of the inclined portion of said casing.

1 0. In apparatus of the character described, a steeping tank adapted to contain a steeping hquor and having a feeding inlet anu a ischarge, means for feeding fibrous material into said feeding inlet, an elevator for removing stepped fibrous material from the discharge and for permitting draining thereof, the drained liquor being returned to said steeping tank, an expeller, means for introducing the drained material into said expeller, and means for returning liquor removed from said drained material by said expeller to said steeping tank.

11. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises subjecting the fibrous material to treatment with a heated chemical liquor at a temperature below the boiling point of the liquor and at substantially atmospheric pressure to remove a substantial portion of the bonding materials and effect softening and wilting of the fibrous material mechanically expressing surplus liquor from the wilted fibrous material, introducing the expressed material into a digester, and subjecting the material to digestion at a higher temperature and pressure in the presence of the retained liquor.

12. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises cooking the fibrous material with .a heated chemical liquor maintained at substantially atmospheric pressure and below the boiling point of the liquor to effect softening andwilting of the fibrous material, removing the fibrous material from the liquor, the removed material carrying retained liquor of which a major portion of the active chemical content has been exhausted, packing the removal material in a digester, and then subjecting the material in the presence of such less active liquor retained with the fibrous material to a digesting treatment at a higher temperature and pressure.

13. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises subjecting the fibrous material to treatment with a heated caustic liquor to effect softening and wilting of the fibrous material with consequent substantial reduction in the packing volume thereof, removing the wilted material from the li uor and expelling surplus liquor therefrom ymechanical pressure, and then introducing the expelled material into a cooking vessel and digesting in the presence of repacked material to a digesting treatment which is controlled to reduce the material to incompletely defibered pulp, and then subjecting the resultant material to the action of a chlorinating agent to further disintegrate the fibrous material into pulp and to reak down remaining shives and fiber bundles of the material.

15. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises heating the fibrous material in alkaline liquor to effect softening and wilting of the material, removing the wilted material from the liquor and expressing surplus liquor therefrom, packing the expressed material in a digester, subjecting the material in the presence of retained liquor and at substantially the expressed consistenc to a digesting treatment which is controlle to reduce the material to incompletely defibered pulp, and then subjecting the resultant material to the action of a chlorinating agent to further disintegrate the fibrous material to pulp.

16. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises heating the fibrous material in an alkali metal hydroxide liquor of a strength less than 6% at substantial-1y atmospheric pressure and below the boiling point of the liquor, the fibrous material being heated in liquor in an amount by weight in excess of eight times the weight of the fibrous material to thereby effect softening and wilting of the fibrous material and to introduce the required amount of chemical into the fibrous material, packing the resultant material in a digester, and then digesting the material in the presence of retained liquor under pressure with steam.

17. In the manufacture of pulp from annual growth fibrous material such as straw,

the method which comprises continuously 1ntroducing fibrous material into a maintained bath of heated chemical liquor open to atmosphere and heated to a temperature below the boilin point of the liquor, movingthe fibrous material relatively to the liquor and through the bath to effect wilting and softening o the fibrous material, continuously removing 5 and heated to a the wilted material from the maintained bath of liquor, expelling a portion of the retained liquor from the removed material, returning expelled liquor to the maintained bath, introducing the expressed fibrous material into a cooking vessel, and heating the material in the presence of its retained liquor and at substantially its expressed consistency under pressure. with steam.

18. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises continuously introducing fibrous material into a maintained bath of heated alkali metal hydroxide liquor of a strength less than 6% open to atmosphere temperature below the boilf ing fiber bundles and shives.

ing point of the liquor, .the maintained bath containing liquor in an amount by weight in excess of eight times the weight of fibrous material therein so that the fibrous material tends to float along in the liquor, moving the fibrous material relatively to the liquor through the bath to effect softening and wilting of the fibrous material, the liquor of the bath progressively decreasing in active caustic content from the portion where the fibrous material is introduced to the portion where the fibrous material is removed, continuously removing the wilted material from the maintained bath of liquor, the rate of moving the material through the bath being such that the liquor being retained in the removed fibrous material has the major portion of its causticity exhausted, expelling a portion of the retained liquor from the removed material to raise it to a consistency in excess of 15%, introducing the expelled material into a cooking vessel and heating the material in the presence of the primarily exhausted retained liquor and substantially at the expelled consistency to a temperature in excess 0 140 C. and under pressure with steam.

19. In the manufacture of pulp from annual growth fibrous material such as straw, the method which comprises continuously introducing fibrous material into a maintained bath of heated chemical liquor open to atmosphere and heated to a temperature below the boiling point of the liquor, moving the fibrous material relatively to the bath to effect softening and wilting of the fibrous material, continuously removing the wilted heating the material. in the presence of re tained liquor under pressure with steam to effect an incomplete defibering thereof, and then subjecting the resultant material to treatment with a chlorinating agent (to fur ther defiber the materlal and reduce remain a 20. In the manufacture of pulpl from annual growth fibrous material suc as straw, the method which comprises impregnating the fibrous material with a heated caustic liquor to effect softening and wilting thereof, packing the wilted fibrous material in a digester and cooking under pressure in the presence of impregnating liquor to reduce the material to incompletely defibered pulp, and then subjecting the material to chlorination to further reduce the fibrous material to pulp and break down remaining shives and' fiber bundles.

In testimony whereof I hereto aifix my signature.

JOHN TRAQUAIR. 

